1. Field of the Invention
This invention relates to an antenna, and more particularly to the new type circuit board antenna for the wireless local area network (LAN) communication.
2. Description of the Related Art
In recent years, the development of communication technology enables people to communicate with each other regardless of distance and time. Information may be transmitted via electrical apparatuses, such as personal computers, notebooks, personal digital assistants (PDA), etc, in a wireless manner. Nowadays, wireless communication applications are very popular in our daily life, such as the wireless mobile phone, the wireless modem, the wireless network card, etc.
Wireless Local Area Network (Wireless LANs) enables users to immediately connect to Internet for browsing information, sending and receiving various data. It is an extension or alternative data communication system besides wired local area networks.
Wireless LANs transmit and receive data over the air using radio frequency (RF) technology for minimizing the need for wired connections. The data being transmitted is superimposed on the RF carrier wave by frequency modulation. Multiple RF carrier waves can exist in the same space at the same time without interference if the RF carrier waves are transmitted on different frequencies.
In a wireless LAN configuration, a transmitter/receiver device, called an access point, connects to the wired network from a fixed location using standard cabling. Further, users can connect to a wireless LAN for transmitting data through a wireless communication device which is installed to electrical apparatuses combining an adapter. Furthermore, the antenna device which is comfortably used in the wireless communication product is used to transmit/receive data. Therefore, antennas are the key components of the circuitry of wireless communication products.
When the antenna is in resonance at a resonance frequency, there will be an electromagnetic (EM) wave excited corresponding to the resonance frequency. The operating length of the antenna is decided by the wavelength (?) of the resonance frequency. The operating length of the conventional antenna used in the wireless communication products, such as the dipole antenna or the micro-strip patch antenna, is one-half of the wavelengths (?/2) of the resonance frequency. Moreover, the impedance of one dipole antenna under this condition is theoretically about 70 ohms resistive, and the dipole antenna generally has the good matching impedance (about 50 ohm resistive) by a matching network, such as gamma match etc. In the other word, the dipole antenna is tuned by adjusting the length of the shorting bar on the gamma match with the variable capacitor half engaged. The gamma match technology involves a small air variable capacitor approximately the given value and an adjustable shorting bar at the terminal connected to the element. In recent years, the planar inverted-F antenna (PIFA) structure has been developed, whose operating length is decreased to one-fourth of the wavelength (?/4) of the resonance frequency.
FIG. 1A and FIG. 1B show the front and back diagrams of the traditional wireless LAN antenna. There are two radiating portions 20, 22, a dielectric material portion 30, and a ground surface 40 with a plurality of holes 50 at the front of the circuit board 10. And there are two radiating portions 120, 122, and a dielectric material portion 130 with a plurality of holes 50 at the back of the circuit board 110. The radiating portions 20, 22, 120, 122 are strip conducting parts with a plurality of holes 50 on the dielectric material portion 30, 130, respectively. The strip conducting parts 20 and 120 are opposite, and the strip conducting parts 22 and 122 are opposite, too. That is, the conduction of the strip conducting part 120 intercommunicates with the conduction of the strip conducting part 20 by holes 50, and the conduction of the strip conducting part 122 intercommunicates with the conduction of the strip conducting part 22 by holes 50. The dielectric materials portions 30, 130 are for isolating the radiating portions 20, 22, 120 122 from the ground surface 40.
Moreover, in U.S. Pat. No. 6,727,854 B2, a planar inverted-F antenna (PIFA) with a first operating bandwidth within the GSM band and a second operating bandwidth within the DCS band is disclosed. The planar inverted-F antenna includes a ground surface, a shorting device, a radiating device coupled to the ground surface through the shorting device, a dielectric material set between the radiating device and the ground surface for isolating the radiating device from the ground surface, and a feeding device set on the ground surface and coupled to the radiating device for transmitting a microwave signal.
As shown in FIG. 2, the radiating device 220 includes three radiating elements. The first and second radiating element can be a meandered metallic strip 221, 222, individually and the third radiating element can be a near-rectangular metallic patch 223. The metallic strips 221, 222, and the metallic patch 223 can be formed with integrity (in an integrated manner, i.e., in one body). In order to decrease the area of the radiating device 220, the metallic strip 221 is meandered around the left side of the metallic patch 223 and the metallic strip 222 is meandered around the right side of the metallic patch 223.
The structure of the traditional wireless LAN circuit board antenna is very simple, but the signal receiving quality is not very good. Thus, there is a need to design a new antenna with better efficiency for improving the data transmission efficiency of the wireless network.